This invention relates to a method and a device for manufacturing a magnetic recording medium and, in particular, to a method and a device for use in depositing a lubricant layer on a magnetic base having a protection layer formed prior to deposition of the lubricant layer.
Recent developments of electronic computers has produced requirements for magnetic recording media of large memory capacity, namely, a high packing density. In order to cope with and respond to such a requirement, various improvements have been introduced regarding the magnetic recording medium itself and the magnetic head driven in relation to the magnetic recording medium. At any rate, a floating head is very often used for increasing the packing density. Such a floating head is made to float over the magnetic recording medium, with a gap left between the head and the magnetic recording medium, by an air pressure resulting from rotation of the magnetic recording medium.
As known in the art, a floating head of a contact start stop type (will be abbreviated to a CSS type head hereinafter) is very effective to reduce or narrow the gap between the CSS type head and the magnetic recording medium. Practically, the gap may be equal to or less than 0.2 micron meter in the CSS type head. This shows that the CSS type head is available for a magnetic recording medium of a high packing density.
Herein, it is to be noted that the magnetic recording medium for the CSS type head has not only a recording zone but also a landing zone. The CSS type head is kept in contact with the landing zone before operation thereof and is detached from or lifted off the landing zone to float over the recording zone each time when the CSS type head is driven for write-in or readout operation of information. Thereafter, the CSS type head is landed on the landing zone again to be brought into contact therewith after the operation.
A magnetic recording medium for such a CSS type head usually comprises a substrate of a nonmagnetic material, such as aluminum, a magnetic layer of, for example, an alloy of Co-Ni, which is deposited on the substrate by vacuum evaporation or the like, and a protection layer of, for example, carbon, on the magnetic layer. Such a combination of the nonmagnetic substrate, the magnetic layer, and the protection layer will be collectively called a magnetic base hereinafter. Moreover, a lubricant layer is also coated on the protection layer so as to avoid damage or flaws which might otherwise occur on the magnetic recording medium due to friction or impact of the CSS type head upon liftoff, or landing of the CSS type head. Therefore, the lubricant layer is indispensable to the magnetic recording layer for the CSS type head.
In Japanese Unexamined Patent Publication Nos. Syo 61-133,029, namely, 133,029/1986, description is made about a method of depositing such a lubricant layer on a protection layer. According to this method, a lubricant of a liquid is deposited on the protection layer by spin coating after it is dripped on the protection layer which is formed on a magnetic layer in a vacuum atmosphere. With this method, the lubricant must be diluted by the use of a solvent. Since the solvent is usually vapored or evaporated at an uneven rate during a drying process of the lubricant, the thickness of the lubricant layer is varied not only at various portions of each magnetic recording medium but also among a plurality of the magnetic recording media.
Alternatively, another method of depositing a lubricant layer is proposed in Japanese Unexamined Patent Publication Nos. Syo 61-214,132, namely, 214,132/1986 and comprises the steps of successively forming a magnetic layer and a protection layer on a nonmagnetic sheet and subsequently heating the nonmagnetic sheet to a temperature not lower than 50.degree. C. Specifically, a combination of the nonmagnetic sheet, the magnetic layer, and the protection layer may be called a magnetic base as mentioned before and is fed from a roll to a drum which is heated at the above-mentioned temperature. Thereafter, the magnetic base is rolled up on another roll. A lubricant layer is deposited on the protection layer by vapor deposition during passage of the nonmagnetic sheet. With this method, it is very difficult to keep the protection layer at a constant temperature during deposition of the lubricant layer because the nonmagnetic sheet is locally heated only when the nonmagnetic sheet is brought into contact with the drum. As a result, the lubricant layer inevitably becomes uneven in thickness.
In any event, the lubricant layer may undulate at the landing zone of the magnetic recording medium due to an uneven thickness of the lubricant layer. Such undulation may give rise to a recessed portion and a ridge portion on the landing zone. Under the circumstances, a contact surface of the CSS type head may be embedded or fall in the recessed portion when the CSS type head is put on the landing zone. The CSS type head can not be readily detached or lifted off from the recessed portion once it falls in the recessed portion on rotation of the magnetic recording medium. This might bring about difficulties of rotation of the magnetic recording medium and liftoff of the CSS type head. It is to be noted that no consideration is made about an atmospheric temperature in the above-referenced Japanese Publication.